Tracing the Mediterranean thermohaline circulation since the last deglaciation: insights from benthic foraminifera and geochemical tracers

The Mediterranean Sea is a relatively small, semi-enclosed basin highly sensitive to global climate variability, where oceanic and atmospheric processes are particularly amplified. As such, it serves as an exceptional natural laboratory for studying climatic changes across different timescales. Marine sediment cores provide a unique archive for reconstructing past environmental conditions, preserving detailed records of climate oscillations that can be explored through a wide range of proxies. Well-documented examples of past climatic and oceanographic changes in the Mediterranean include the preservation of sapropels and organic-rich layers in deep sediments, which are associated with major deoxygenation events. Despite decades of extensive research, the causes of these events and their basin-wide impacts on the Mediterranean thermohaline circulation system remain incompletely understood, particularly at intermediate depths. This thesis investigates the properties of mid-depth water masses in the western Mediterranean, aiming to advance knowledge of their natural variability and their role in connecting the two Mediterranean basins during deglacial and Holocene climatic changes. To this end, we focus on two sediment cores from the western Mediterranean, one from the southern Alboran Sea (~370 m) and another from the northeastern Ligurian Sea (~432 m). A high-resolution multi-proxy approach has been applied to provide a detailed characterization of the paleoenvironmental conditions in both regions, integrating sedimentological, geochemical, and micropaleontological tools. The research presented here provides new insights into the key factors controlling coral mound development in the Alboran Sea over the last deglaciation, suggesting that increased particulate organic matter serves as a primary driver, while oxygen availability does not act as a limiting factor. This thesis also contributes to advancing our understanding of past oceanographic patterns in the Ligurian Sea by focusing on benthic foraminiferal assemblages, a largely unexplored component of the region. Findings reveal intensified melting of Northern Apennines glaciers during Heinrich Stadial 1 and highlight the potential role of dense shelf-water formation processes throughout the Early Holocene. Lastly, comparable changes in intermediate water mass properties in the Alboran and Ligurian sub-basins provide the basis for proposing, for the first time, the formation of a western-sourced intermediate water mass during the last sapropel deposition in the eastern basin, which likely played a key role in promoting mound development in the Alboran Sea.